This invention generally relates to peristaltic pumps for transporting or pumping fluids. More specifically, this invention relates to an improved peristaltic pump using a pumptube comprising a single tube of a relatively rigid and hard fluoroplastic material, preferably relatively rigid and hard polytetrafluoroethylene (PTFE), and a roller strap located between the pressure rollers of the peristaltic pump and the pumptube. The pumping section of the pumptube, which is not directly contacted by the pressure rollers of the peristaltic pump, is pre-formed or shaped into a flaftened cross section with an overall U-shape which approximately conforms to the pumptube passageway in the peristaltic pump. The pressure rollers contact the roller strap and then compress the flattened side of the pumptube and, thereby, effect transport or pumping of the fluid. The use of the strap prevents excessive tube expansion at the output back-pressure, thereby increasing the lifetime of the pumptube. Using the pumptubes and peristaltic pumps of this invention, corrosive, viscous, sensitive, biological, and/or high pressure fluids can be readily handled. Moreover, fluids up to about 50xc2x0 C. can be pumped at a back-pressure up to about 4 bar; higher operating temperatures may be possible with lower back-pressures. The pumptube and peristaltic pumps of this invention are especially adapted to operate against high back- or counter-pressures.
Peristaltic pumps are preferred for certain applications where it is desirable to pump measured amounts of a fluid or to pump a fluid through tubing while avoiding contact between pump components and the fluid being pumped. In a typical peristaltic pump system, a length of tubing is contacted by a series of pressure rollers that rotate in a circular path. The pressure rollers contact and progressively compress a flexible pumptube at spaced intervals against a surface or raceway so as to flatten or locally reduce the cross-sectional area of the fluid passageway in the pumptube. Preferably, the cross-sectional area of the fluid passageway is effectively reduced to zero (i.e., complete occlusion) as each pressure roller moves over the pumping section of the pumptube. As the pressure rollers continue to roll over the pumptube, the successive flattened portions expand or return to the original cross-sectional area due to the resilience of the tube which generates a sub-atmospheric pressure in the fluid passageway to draw the fluid therein.
The efficiency and operating characteristics of a peristaltic pump generally depend on the physical and chemical characteristics of the pumptube. The pumptube generally must have a combination of properties including flexibility, resilience, durability, resistance to creasing, and resistance to adverse chemical or physical effects, since the pump may be used to pump diverse materials including acids, alkali, solvents, toxic, and sterile liquids.
Commercially available peristaltic pumptubes are generally uniformly cylindrical, flexible tubes with a uniform wall thickness which provide a fast recovery rate of the flattened portion to the normal cross-sectional area. Such pumptubes are normally formed from resilient elastomeric materials such as natural rubber, silicone, polychloroprene, and polyvinyl chloride. Such materials, however, have limited resistance to chemical degradation. Moreover, such materials may leach components (e.g., softening agents and the like) into the fluid being pumped and/or absorb components from the fluid being pumped. Thus, the use of pumps using such pumptubes is generally restricted to liquids having minimal degradation effects.
Fluoroplastic tubing, which has good corrosion resistance, generally has been found to lack resilience and tends to crease in use, thereby limiting the life of such tubing. U.S. Pat. No. 3,875,970 (Apr. 8, 1975) attempted to overcome this problem by providing a pumptube having a thin inner tubular portion of a corrosion resistant material (such as polytetrafluoroethylene) and a thicker outer tubular portion of a resilient elastomeric material (such as silicone, polychloroprene, flexible polyvinyl chloride, natural or synthetic rubber). The overall pumptube remained flexible. Although the design of this pumptube reportably extended the life of the tubing, it has not been as successful as desired and its use in commercially available peristaltic pumps appears to be very limited.
In addition, a variety of pumptubes incorporating various geometric configurations, including multiple layered tubes, have been used in peristaltic pumps. U.S. Pat. No. 3,105,447 (Oct. 1, 1963) used a double layered pumptube where both the inner and outer tubes consisted of rubber or an elastomer. The pumptube design allowed a lubricant to be pumped through the space formed between the inner and outer tubes. German Patent 3,322,843 A1 (published Jan. 3, 1985) also provided a double layered pumptube with a particularly soft and elastic inner layer and an impermeable outer layer. The inner layer could be formed of silicone, natural rubber, soft polyvinyl chloride, polyurethane, or fluoroelastomer; the outer layer could be formed of polyvinyl chloride, polyurethane, fluoroelastomer, and certain polyethylenes. The pumptube was flexible and maintained a circular cross-section in the uncompressed state. European Patent Publication 0,470,33 A1 (published Feb. 12, 1992) provided a flexible pumptube with an elastic reinforcing member or members disposed therein to reduce fatigue failure upon repeated compression and recovery of the tubing. U.S. Pat. No. 5,067,879 (Nov. 26, 1991) provided a flexible, single- or multi-layered pumptube having two longitudinally extending notches or groves in the outer surface. The groves were reported to improve the flexing characteristics of the tubing during compression and recovery. Although providing useful and significant advances in the art, each of these just described pumptubes has significant limitations for use in peristaltic pumps, especially for peristaltic pumps for corrosive and other difficult to handle liquids.
More recently, U.S. Pat. No. 5,482,447 provided a double layer pumptube having a inner tube and an outer tube, both of which were preferably polytetrafluoroethylene (PTFE). Although this pumptube was a significant advance over the prior art, the pumptube, largely because of its tube within a tube design, was more costly and difficult to manufacture than desired. Additionally, the pumptube""s useful lifetime was not as high as desired when operated against a significant back-pressure.
The present invention provides an improved peristaltic pump and an improved pumptube. Using the peristaltic pump of this invention, a single shaped tube of rigid fluoroplastic material (preferably PTFE) can be used. Thus, many of the advantages obtained in the double layered PTFE pumptubes of U.S. Pat. No. 5,482,447 can be obtained using a significantly simplified pumptube (i.e., single tube construction) as provided herein. The pumptube and peristaltic pump of the present invention are especially adapted for use in systems which develop, or can develop, high back- or counter-pressures. Using the present system, peristaltic pumps can operate continuously to pump liquid against a counter-pressure of at least 4 bar at a flow rate of at least 4 liters per minute (LPM).
The present invention relates to an improved peristaltic pump using a pumptube comprising. a single tube of relatively rigid and hard fluoroplastic material, preferably relatively rigid and hard polytetrafluoroethylene (PTFE), and a roller strap located between the pressure rollers of the peristaltic pump and the pumptube. The roller strap is an inelastic material such as, for example, a polyester, an aromatic polyamide, or the like. Preferably, the roller strap is an aromatic polyamide because of its reduced tendency to form a xe2x80x9chammockxe2x80x9d during operation. One especially preferred aromatic polyamide is KEVLAR(trademark) (DuPont). A KEVLAR(trademark) strap coated with polychloroprene on both flattened sides is even more preferred; one especially preferred strap is a 1 mm thick KEVELAR(trademark) strap coated with 0.2 mm of polychloroprene on both flattened sides. The combination of the pumptube and the roller strap allows for improved performance, especially with regard to pumptube lifetime, when operating at relatively high back- or counter-pressure. The present pumptube and peristaltic pump can also be used when such back-pressures are not generated or are not likely to occur.
The pumping section of the pumptube is preformed or shaped into a flattened, oval-like shape (e.g., a flattened U-shape as shown in FIG. 2) which approximately conforms to the occlusion bed or pumptube passageway in the peristaltic pump. The pressure rollers contact the strap, rather than the pumptube itself, and thereby compress the flattened side of the pumptube and effect the transport or pumping of the fluid. The pressure rollers do not directly contact the pumptube since they are separated from the pressure rollers by the roller strap. The inner surface of the flattened fluid passageway is required to move only a relatively short distance when compressed by the pressure rollers. Moreover, the flatten portion of the pumptube is contained on its outer side by the pumptube passageway and on its inner side by the strap. The movement of the pumptube during compression is thus limited. Moreover, the strap prevents excessive expansion of the pumptube, especially in the roll-off section, when operated against a high back- or counter-pressure. Thus, the placement of the strap between the rollers and the pumping section of the pumptube prevents excessive expansion of the pumping section between the rollers themselves and between the last roller and the outlet end, especially when exposed to a significant back or counter pressure. Preferably, the strap rests on guide cams on both the roll-on and roll-off portions of the pump to further limit expansion of the pumptube in the roll-on and/or roll-off portions. Thus, the materials forming the pumptube remain within their elastic fatigue limits, even when operated against high back-or counter-pressure, thereby significantly reducing fatigue failure and significantly increasing the lifetime of the pumptube. The pumptube systems and peristaltic pumps of this invention are especially adapted for situations where the back- or counter-pressure may vary over time. The pumptube systems and peristaltic pumps of this invention can be used for pumping and transporting corrosive, viscous, sensitive, biological, and/or high pressure fluids at high flowrates and against significant back- or counter-pressure.
The present invention provides a peristaltic pump for transporting fluids, said peristaltic pump comprising
(a) a pump housing containing a pumptube passageway;
(b) a pumptube to fit within the pumptube passageway, the pumptube having inlet and outlet ends extending outside the pump housing, a pumping section contained within the pumptube passageway, and a fluid passageway extending through the pumptube from the inlet end to the outlet end;
(c) a plurality of pressure rollers rotatably mounted within the housing, whereby each roller in turn compresses the pumping section of the pumptube contained within the pumptube passageway so as to transport fluid from the inlet end to the outlet end of the pumptube;
(d) a guide cam attached to the pump housing to support the pumping section of the pumptube adjacent to the outlet end; and
(e) a strap mounted between the plurality of pressure rollers and the pumping section of the pumptube and between the guide cams and the ends of the pumping section of the pumptube so that the pressure rollers are able to compress the pumping section without directly contacting the pumping section;
wherein at least the pumping section of the pumptube comprises a single rigid fluoroplastic tubing preformed to fit within the pumptube passageway such that the pumptube within the pumping section is flattened into an oval-like shape with an oval-shaped fluid passageway such that the pressure rollers compress the pumping section of the pumptube essentially along the flattened side of the oval-like shape without contacting the pumping section. Preferably, the pump housing also has a guide cam to support the pumping section of the pumptube adjacent to the inlet end.
The present invention also provides a peristaltic pump for transporting fluids, said peristaltic pump comprising
(a) a pump housing containing a pumptube passageway;
(b) a pumptube having inlet and outlet ends extending outside the pump housing, a pumping section contained within the pumptube passageway, and a fluid passageway extending through the pumptube from the inlet end to the outlet end;
(c) a plurality of pressure rollers rotatably mounted within the housing, whereby each roller in turn compresses the pumping section of the pumptube contained within the pumptube passageway so as to transport fluid from the inlet end to the outlet end of the pumptube; and
(d) a strap mounted between the plurality of pressure rollers and the pumping section of the pumptube so that the pressure rollers are able to compress the pumping section without contacting the pumping section;
wherein at least the pumping section of the pumptube comprises a single rigid fluoroplastic tubing preformed to fit within the pumptube passageway such that the pumptube within the pumping section is flattened into an oval-like shape with an oval-shaped fluid passageway such that the pressure rollers compress the pumping section of the pumptube essentially along the flattened side of the oval-like shape without contacting the pumping section. Preferably, guide cams are attached to the pump housing to provide support to the strap near and/or at end of the roll-on and roll-off sections of the peristaltic pump.
The present invention also provides a pumptube system comprising a pumptube and a roller strap, which system is suitable for use in a peristaltic pump having a pumptube passageway and a plurality of pressure rollers for compressing the pumptube whereby a fluid can be transferred, wherein the pumptube comprises
(a) inlet and outlet ends;
(b) a pumping section located between the inlet and outlet ends; and
(c) a fluid passageway extending through the pumptube from the inlet end to the outlet end;
wherein at least the pumping section of the pumptube comprises a single rigid fluoroplastic tubing, wherein the pumptube is preformed to fit within the pumptube passageway such that the pumptube within the pumping section is flattened into an oval-like shape with an oval-like fluid passageway such that the pressure rollers compress the pumping section of the pumptube essentially along the flattened side of the oval-like shape;
and wherein the roller strap comprises an inelastic material located between the pressure rollers and the pumping section of the pumptube so that the pressure rollers do not contact the pumping section of the pumptube when the pumping section is compressed.
The present invention also provides a method of preparing a pumptube suitable for use in a peristaltic pump having a pumptube passageway, wherein the pumptube has a flattened, oval-like shaped pumping section with an oval-like fluid passageway, a plurality of pressure rollers, an inelastic strap located between the pressure rollers and the pumptube, wherein the pressure rollers, through pressure transferred though the strap, compress the pumptube via the strap without directly contacting the pumptube, whereby a fluid can be transferred, said method comprising
(a) forming a length of a rigid fluoroplastic tubing having a fluid passageway extending throughout the length of the rigid fluoroplastic tubing;
(b) placing a central portion of the length of rigid fluoroplastic tubing in a clamping fixture capable of compressing the central portion;
(c) compressing the central portion of the rigid fluoroplastic tubing at or near room temperature using the clamping fixture to form a fully compressed and flattened section in the central portion;
(d) allowing the fully compressed and flattened section to expand to form the flattened, oval-like shaped pumping section with the oval-like fluid passageway therein;
(e) heating at least the pumping section of the rigid fluoroplastic tubing to a temperature sufficient to increase the malleability of the rigid fluoroplastic tubing;
(f) placing the heated rigid fluoroplastic tubing in a molding fixture capable of molding the pumptube into a shape to fit within the pumptube passageway;
(g) molding the pumptube into the shape to fit within the pumptube passageway without obstructing the oval-like fluid passageway; and
(h) allowing the pumptube to cool to or near ambient temperature within the molding fixture;
whereby the pumptube fitting within the pumptube passageway of the peristaltic pump is obtained. Preferably a core is placed within the fluid passageway during the molding step to help maintain the desired cross-section within the oval-like fluid passageway and to prevent obstructing the oval-like fluid passageway. Alternatively, gas under pressure can be pumped through the fluid passageway during the molding step to achieve the same effect. Of course, such a core would be placed within the fluid passageway before step (e) and then removed after step (h).
These and other embodiments and advantages of the present invention will be apparent from a consideration of the present specification and drawing.